THE COAST-FLORA OF THE CLACTON DISTRICT. 205
(2.) The vegetation of the grey dune, the "conquered land,"
where the sand is fixed by a continuous carpet of plants.
The representative plant of the white dune is Psamma aren-
aria (Sea Marram). It grows in scattered tufts, each of which
gives rise to a small sand-hill, which is held together by a
very extensive system of rhizomes. Thus it becomes itself
one of the chief agents in forming the elevated dunes. Of course
Clacton does not offer any high or extensive dune, but just
enough to study the main characteristics of its vegetation.
The chief dangers to which plants on such sites are exposed
are : (1) drought, (2) being laid bare, dechausse the French call
it, (3) being buried, (4) being injured by the flying grains of
sand or by the wind directly. It is a very striking lesson to
notice with what diversity of means different plants meet the
same difficulties. Here we find Eryngium maritimum (Sea
Holly), unfortunately disappearing in those parts which are
within reach of the more idle of the sea-side visitors ; its immense
stock in the sand, its stiff, conations, bluish leaves need no
explanation. Convolvulus soldanella with its beautiful red
flower, slightly winding stem, glossy leaves, and Arenaria pep-
loides (another Sea-Purslane), a low succulent annual, I need
only mention. Perhaps flie most interesting of all anatomical
peculiarities is the rolling-mechanism of the grass-leaves, notably
in Psamma, but also in the other dune grasses, and in Spartina
stricta (Bristle-grass).
However, the vegetation soon conquers the feeble dune,
and the so-called grey-dune vegetation arises. Marram grass
and Sea Holly disappear, choked apparently by too many
competitors. The chief characteristics of this association are
lowness of growth and continuity. Plantago coronopus, Leon-
todon autumnale, Hypochaeris radicata form rosettes, Armeria
vulgaris (Thrift) becomes sometimes even a cushion-plant ;
its root is richly ramified and bears a rosette of narrow leaves on
every branch, the whole forming a hemispherical cushion ; the
stem of Silene maritima (Sea Campion) is decumbent ; mosses
and lichens, of course, fit in with the general character. The
obvious cause of the clinging to the ground is the necessity of
holding the sand together. Incidentally this growth-form pro-
tects them from the full force of the wind and keeps the moisture
back in the soil. Rosettes are said to be caused by rapid altera-